Pattern repeats add a variable to knitting math. The basic factors in knitting math are the stitch count per inch, and the row count per inch. But what about the pattern repeat? In this example, we'll work in the round, so the repeat has to line up exactly.
These mittens are my everyday winter mittens. They have a "pattern repeat" of 4 stitches (2/3 of an inch, or .6666). The stitches per inch is 6. What does that matter? Well, you'll need both numbers if you need to adjust the pattern to fit some other size. Pattern repeat = 4 stitches in 2/3 of an inch. Stitch count = 6 stitches per inch.
My hand and the gauge and the original pattern all work out to the same size (I wear a mitten that's 8.25 inches around) so it works out nicely. But my husband's hand is larger than the original pattern, so for him I'll have to modify to make it fit. If I only mind the stitches per inch (6), my mitten will have a weird jog in it where the pattern doesn't line up, because the pattern repeats in 4s , not 6s. The mittens are stranded, which keeps them from being very stretchy, so I can't rely on stretch to save me if they're a little small. What to do?
Well, the pattern repeat of 4 stitches = 2/3 of an inch. If I measure my husband's hand, I discover that he needs a mitten that's 9.4 inches around. If I take a look at the original pattern, I see that the pattern repeats 12 times in 8.25 inches (or six times on the front and six on the back). Now I need to subtract 8.25 inches (pattern size) from 9.4 inches (the size I need for my husband). I get 1.15 inches that need to be added to make a mitten to fit the hubby. Size I have - size I need = amount of room I need to add (or subtract).
If I divide that 1.15 extra that I need by the pattern repeat of .6666 inches, I get 1.75, or one and three quarters of a repeat. That means I need 7 more stitches around to make the mitten exactly my husband's size. One more stitch (8 stitches) gives me a perfect pattern repeat of 2 (4 stitches in the repeat twice), or only one extra stitch over the entire circumference of the mitten. I can work with that! So, to make the mittens for my husband, I would need to add 8 stitches to the pattern, and just work those repeats in with the original pattern. I can work the decreases at the top by starting them at the tip of the hubby's little finger, and follow the decreases a few extra times until I run out of stitches.
Amount of change in inches / length of pattern repeat in inches = number of pattern repeats needed.
Number of pattern repeats needed x pattern repeat in stitches = number of stitches to add.
The thumb is a pattern repeat of 2 (which is 1/3 of an inch), so that math is really easy. I measure the original, subtract that measurement from the hubby's thumb measurement, and discover I need 3/4 of an inch extra. That's 4 and 1/2 stitches. I can afford to be a stitch short or a stitch over, so I choose over. (Tight thumbs stink!) I round the 4.5 stitches I need up to the next even number (6) to accommodate the pattern repeat, and I'm done.
Short pattern repeats give you more flexibility to modify size than long ones, but we'll work with long ones in the next article. Knitting math isn't hard if you know the formulas and you have a calculator. You can do it!